Mortality of Marbled Murrelets Due to Oil Pollution in North America

Mortality of Marbled Murrelets (Brachyramphus marmoratus) due to oil pollution is one of the major threats to murrelet populations. Mortality from large spills and chronic oil pollution has been occurring for several decades but has been documented poorly throughout their range; it probably has contributed to declines in populations, in conjunction with loss of nesting habitat and mortality in gill nets. The 1989 Exxon Valdez oil spill in Alaska caused the largest single mortality of murrelets (about 8,400 birds) in the world and contributed to decline in murrelet populations in Prince William Sound. Due to inadequate baseline data, low recovery of oiled carcasses, and other factors, the full impacts of this extensive mortality have not been determined. Restoration activities have included acquisition of murrelet nesting areas in old-growth forests in southcentral Alaska. Similar acquisition of old-growth forests will occur as restoration for mortality from the 1986 Apex Houston oil spill in California. Future oil spills will continue to threaten the viability of small, declining populations, especially in California, Oregon and Washington where a single large spill could extirpate an entire population. Efforts must be expanded to: better document mortalities during large and small spills, develop better baseline data to assess impacts, identify old-growth forests for acquisition for restoration, and reduce oil pollution. Large oil spills have killed millions of seabirds around the world in this century, as recently demonstrated during the 1989 Exxon Valdez spill in Alaska (Ford and others 1991a, Piatt and Lensink 1989, Piatt and others 1990a). In particular, oil pollution poses a significant threat to Marbled Murrelets (Brachyramphus marmoratus) in Alaska, British Columbia, Washington, and California (Carter and Morrison 1992, King and Sanger 1979, Marshall 1988a, Sealy and Carter 1984, Wahl and others 1981). Large numbers of Marbled Murrelets were killed during the Exxon Valdez spill, and this has increased concerns. Large oil spills result periodically from: oil tanker and barge mishaps (groundings, collisions, explosions, accidental spillages); similar mishaps by other large ocean-going vessels; offshore oil wells (well blow-outs, accidental spillages); unloading and loading cargo from onshore and offshore facilities; and onshore facility spills that enter the ocean. In addition, small oil spills occur frequently in many populated areas due to cleaning of tanks at sea, bilge pumping and smaller accidental spills. All types of boats and marine transportation vessels may be involved. Other forms of marine pollution that may affect seabirds are considered by Fry (this volume). Impacts of large oil spills on seabirds in California, Oregon, and Washington have been well-documented during the last 25 years, and sporadically in earlier years. Widespread concern about the effects of oil spills on seabirds along the west coast developed after the 1969 Santa Barbara and 1971 San Francisco oil spills in California and smaller spills in Washington. These spills followed similar events in Europe such as the 1967 Torrey Canyon spill in the western English Channel (Bourne and others 1967). Since the 1970s, the documentation of oil spills and their impact on seabirds has been much improved. Impact assessment is now formalized within Natural Resource Damage Assessment (NRDA) legislation. When possible, the numbers of birds affected are enumerated and impacts at the population level are determined. Impacts include: the direct deaths of birds found dead on shore; deaths of birds found alive on shore and taken to rehabilitation centers; deaths of birds at sea and on shore that are not directly enumerated; reductions in numbers of breeding birds; reductions in breeding range; reduced breeding success; and the sublethal effects of oiling for birds that survived initial oil contamination whether rehabilitated or not. When the full impacts of oil pollution are considered, lethal and sublethal impacts may have profound effects on local populations, especially when oil mortality acts in concert with other anthropogenic and/or natural factors affecting populations (Piatt and others 1991, Swartzman and Carter 1991, Takekawa and others 1990). However, population impacts are often difficult to demonstrate because they usually require detailed pre-event baseline data, careful injury determination, and detailed follow-up data after the event. In this paper, we review documentation of mortality of Marbled Murrelets due to oil pollution throughout their range in North America. In particular, we have focused on providing a summary of mortality and restoration efforts after the 1989 Exxon Valdez spill in Alaska and details of mortality for several smaller spills in California, Oregon, Washington, and British Columbia, where the species in now listed as threatened. Information for the three southern states was collated for the Marbled Murrelet Recovery Plan (U.S. Fish and Wildlife Service, in press). Exxon Valdez Oil Spill The largest single event of Marbled Murrelet mortality from oil pollution in North America was the Exxon Valdez oil spill in Prince William Sound, Alaska. On 24 March 1 Wildlife Biologist, National Biological Service, U.S. Department of the Interior, California Pacific Science Center, 6924 Tremont Road, Dixon, CA 95620 2 Wildlife Biologist, U.S. Fish and Wildlife Service, Migratory Bird Management, 1011 East Tudor Road, Anchorage, AK 99503 Chapter 26